1. Field of the Invention
The present invention relates to an image forming apparatus and an image forming method, and more particularly to an image forming apparatus and an image forming method in which an image is formed on an image formation body by using an ink and a treatment agent.
2. Description of the Related Art
In the inkjet recording system, the recording is performed by ejecting ink droplets onto a recording medium. By contrast with other systems, noise during the recording operation is low, running cost is low, and image recording with high resolution and high quality can be performed. The ink ejection system can be a piezoelectric system using the displacement of a piezoelectric element or a thermal system using thermal energy generated by a heat-generating element.
However, the problem associated with the inkjet recording system is that where the adjacent ink droplets (dots) overlap to each other when the ink droplets are continuously deposited onto the recording medium, the so-called landing interference (bleeding) occurs, namely, the ink droplets forming the adjacent dots merge under the effect of surface tension on the recording medium and dots of desired shape and size cannot be formed. Where the aforementioned landing interference occurs, when the dots have the same color, the shape of dots collapses, and when the dots of different colors are obtained, not only the dot shape collapses, but also colors are mixed.
A two-liquid aggregation system using a treatment liquid that reacts with ink and causes the ink to aggregate has been suggested as means for preventing such landing interference occurring between the ink droplets on the recording medium. For example, Japanese Patent Application Publication No. 2004-010633 discloses a technology that improves optical density, oozing, oozing between colors (bleeding), and drying time in the two-liquid aggregation system by imparting acidic properties to one liquid from among the liquid composition (treatment liquid) and ink and imparting alkaline properties to the other and controlling the aggregation ability of the pigment on the recording medium.
However, if a layer of the treatment liquid is present on the recording medium, then the ink droplets deposited onto the treatment liquid layer float inside the treatment liquid layer and hence the ink coloring material moves. As a result of this, a problem arises in that the output image is disturbed significantly with respect to the desired image. Furthermore, if the treatment liquid permeates into the image receiving layer of the recording medium after the deposition of the treatment liquid on the recording medium and before the deposition of ink droplets, then a sufficient aggregating reaction does not occur on the surface of the recording medium, and hence there is also a problem in that a bleeding prevention effect is not obtained.
In particular, in a system where the deposition of the treatment liquid and the deposition of the ink droplets are performed by independent line heads, a time period of the order of several seconds is required from the deposition of the treatment liquid onto the recording medium until the deposition of the ink droplets, and hence a portion of the treatment liquid permeates into the recording medium and it is not possible to form an aggregating treatment liquid layer of sufficient volume on the surface of the recording medium. Moreover, if ink droplets are continuously ejected at high speed in such a manner that a plurality of ink droplets are mutually overlapping on the recording medium (for example, at a droplet ejection interval of 10 to 50 microseconds), then the aggregating reaction of the ink droplets that have been previously deposited cannot proceed sufficiently rapidly, and bleeding occurs.